Overpressuring is one of the major causes of energy waste in water systems. Many water systems function adequately but at pressures in excess of those needed to move water through the system. This energy waste is commonly suffered by special purpose systems designed to supply water, or other working liquid, to an elevated structure such as an office building.
For example, the typical high-rise office building has its own pumping system, which is fed by water delivered from a standard city water system. The building pumping system takes this water and pumps it up to a delivery point to an elevated location, where it is used. The pumping system must add sufficient energy to the stream to elevate the water and overcome frictional losses enroute to the delivery point. Upon arrival at the delivery point the water must be pressurized to a pressure sufficient for the intended use.
In general, it may be difficult to predict the actual flow and head requirements for the pumping system, and therefore the pumps are frequently overdesigned. Typically the pump system designer is familiar with system head curves, which relate pump head requirements to system flow but he must use empirical data and formulas to calculate the frictional losses which will be encountered in this system. Moreover, the frictional losses, and hence the system head curve, will vary from time to time with aging of the system and incorporation of minor modifications in the lines. Thus the calculated system head curve heretofore may have differed appreciably from the actual system head curve of a water system.